This seems to be based not on hard fact, but on some sketchy back of the envelope calculation using Ocampa lifespans + the 500 generations statement. Waaay too far out in original research territory. I'll only post here, but the date has spread to a number of pages and I intend to purge it wherever I find it. -- Capricorn (talk) 14:27, February 5, 2016 (UTC)

The ruling family of the Ramatis system are discovered to lack the gene required for the sense of hearing. A system is developed in which the members of the ruling family may both hear and speak through a "chorus" of interpreters. (TNG: "Loud As A Whisper")

"Our way of communicating has developed over the centuries". I can't find a more specific date. Star Trek Chronology (p9) also indicates "the arrangement has lasted for centuries."